Remove dependencies incompatible with Python 3

Removed futures and argparse since they are not available on Pypi for Python 3+

requirements.txt

 wheel>=0.23.0
 Cython>=0.20.2
-argparse>=1.2.1
-futures>=2.1.6
 six>=1.7.3
 gensim>=1.0.0
 scipy>=0.15.0